A railroad freight car draft gear assembly has been used for many years at opposite ends of a railcar to absorb and cushion impact forces directed against and to the railcar. Most railcar draft gear assemblies include a housing having an inner tapered bore at an open end, an elongated spring disposed within the housing, a series of metal friction shoes or members arranged in the tapered bore of the housing and movable against the spring upon compression of the draft gear assembly, and a wedge or actuator disposed in operable combination with the friction members such that impact blows directed against the wedge are transferred axially to the spring and radially to the housing. In most railcar draft gear assemblies, a spring seat is arranged between an end portion of each friction member and the spring.
Recently, elastomeric materials have been used and accepted as replacements for steel springs. One elastomeric spring assembly offering beneficial results is disclosed in U.S. Pat. No. 5,351,844 to R. A. Carlstedt and includes multiple elastomeric spring units stacked in axial relation relative to each other. Each spring unit of the spring assembly includes an elastomer pad sandwiched between two metal plates. The metal plates are bonded or otherwise secured to opposed faces of the elastomer pad. Amongst other advantages, the metal plates serve to limit snaking and/or buckling problems while furthermore serving to center elastomeric spring assembly relative to the draft gear housing. Such a spring assembly has been successfully used for years in combination with railcar draft gears.
In one form, the draft gear housing is provided with an elongated opening between the closed end and open end of the housing and extending along a sidewall of the draft gear housing to allow the spring units to be inserted and stacked relative to each other within the draft gear housing. Maintaining the spring units in alignment relative to each other and generally centered relative to the longitudinal axis of the draft gear assembly is an important consideration when designing a railcar draft gear assembly. Moreover, maintaining the elongated spring assembly in relatively centered relationship relative to the longitudinal axis of the draft gear is also important to overall performance of the draft gear assembly.
The draft gear assembly is arranged within a pocket in the railcar and extends generally parallel to a longitudinal axis of the railcar. Accordingly, when the railcar travels through a curve, the railcar tends to impart unequal forces to the draft gear assembly. Such unequal forces applied to the draft gear assembly are also frequently transferred to the elongated spring assembly tending for the individual spring units to become misaligned relative to each other and relative to the longitudinal axis of the draft gear. As mentioned, displacement of the individual spring units relative to each other and relative to the longitudinal center of the draft gear assembly can result in undesirable overall performance of the railcar draft gear assembly.
Railcar manufacturers and suppliers for supplying such railcar manufacturers are continually seeking methods and ways of reducing the manufacturing costs of railcars and the components used to build such railcars without having to sacrifice performance and quality. When considering costs savings in connection with a draft gear assembly, however, the available options are few. First, the size of the draft gear housing cannot be changed without adversely affecting the relationship of the fixed size pocket in a railcar centersill wherein the draft gear assembly is accommodated. Second, and with the size of the draft gear assembly being standardized or fixed, the amount of steel used to form the draft gear housing has already been minimized as with openings and voids wherever possible. Exacerbating these design challenges is the fact that speeds of railcars are steadily increasing, thus, adding to the impact loads imparted to the draft gear assembly during railcar operation. As such, the size of the spring assembly used to absorb, dissipate and return energy imparted thereto during railcar operations cannot be reduced without adversely affecting performance and operation of the draft gear assembly.
Thus, there remains a continuing need and desire to provide a railcar draft gear which is economically designed to have high shock absorbing capacities while offering enhanced performance by maintaining the spring units of the elongated spring assembly in aligned relation relative to each other and relative to the longitudinal axis of the draft gear assembly.